The present invention relates to a method of obtaining and selecting monoclonal antibodies using an assay of the ADCC type, said antibodies being capable of activating Fcγ type III receptors. The invention is also directed toward monoclonal antibodies having a particular glycan structure, the cells producing said antibodies, the methods for preparing the producer cells, and also the pharmaceutical compositions or the diagnostic tests comprising said antibodies. The anti-D antibodies according to the invention can be used for preventing Rhesus isoimmunization of Rh-negative individuals, in particular a hemolytic disease of the newborn (HDN), or in applications such as Idiopathic Thrombocytopenic Purpura (ITP).
Passive immunotherapy using polyclonal antibodies has been carried out since the 1970s. However, the production of polyclonal immunoglobulins poses a problem: The immunization of volunteers was discontinued in France in 1997 because of the ethical problems that such acts present. In France, as in Europe, the number of immunized donors is too low to ensure a sufficient supply of certain antibodies, to such an extent that it proves necessary to import hyperimmunized plasma from the United States for example.
Thus, this immunoglobulin shortage does not make it possible to envisage antenatal administration for preventing HDN.
Various studies have resulted in the production of human monoclonal antibodies for the purpose of replacing the polyclonal antibodies obtained from fractionating plasmas from voluntary donors.
Monoclonal antibodies have several advantages: they can be obtained in large amounts at reasonable costs, each batch of antibodies is homogeneous and the quality of the various batches is reproducible since they are produced by the same cell line, which is cryopreserved in liquid nitrogen. It is possible to ensure the safety of the product with regard to an absence of viral contamination.
Several publications describe the production of cell lines producing human anti-Rh D monoclonal antibodies of IgG class, from B cells of immunized donors. Boylston et al. 1980; Koskimies 1980; Crawford et al. 1983; Doyle et al. 1985; Goossens et al. 1987; Kumpel et al. 1989(a) and McCann-Carter et al. 1993 describe the production of B lymphocyte lines transformed with the EBV virus. Melamed et al. 1985; Thompson et al. 1986 and McCann-Carter et al. 1993 relate to heterohybridomas resulting from B lymphocyte (transformed with EBV)×murine myeloma fusion. Goossens et al., 1987 relates to heterohybrids resulting from B lymphocyte (transformed with EBV)×human myeloma fusion. Bron et al., 1984 and Foung et al., 1987 describe heterohybrids resulting from B lymphocyte (transformed with EBV)×human-mouse heteromyeloma fusion and, finally, Edelman et al., 1997 relates to insect cells transfected with the gene encoding an anti-Rh(D) using the baculovirus system.
Among the patents and patent applications relating to such monoclonal antibodies and the lines secreting them, mention may be made of: EP 576093 (AETS (FR), Biotest Pharma GmbH (Germany); Composition for prophylaxis of the haemolytic disease of the new-born comprises two human monoclonal antibodies of sub-class IgG1 and IgG3, which are active against the Rhesus D antigen), RU 2094462, WO 85/02413 (Board of Trustees of the Leland Stanford Jr. University, Human Monoclonal Antibody against Rh (D) antigen and its uses), GB 86-10106 (Central Blood Laboratories Authority, Production of heterohybridomas for manufacture of human monoclonal antibodies to Rhesus D antigen), EP 0 251 440 (Central Blood Laboratories Authority, Human Anti-Rhesus D Producing Heterohybridomas), WO 89/02442, WO 89/02600 and WO 89/024443 (Central Blood Laboratories Authority, Human Anti-Rh (D) Monoclonal Antibodies), WO 8607740 (Institut Pasteur, Protein Performance SA, Paris, FR, Production of a recombinant monoclonal antibody from a human anti-rhesus D monoclonal antibody, production thereof in insect cells and uses thereof), JP 88-50710 (International Reagents Corp., Japan, Reagents for Determination of Blood Group Substance Rh (D) Factor), JP 83-248865 (Mitsubishi Chemical Industries Co., Ltd., Japan, Preparation of Monoclonal Antibody to Rh (D) positive Antigen); CA 82-406033 (Queens University at Kingston, Human Monoclonal Antibodies) and GB 8226513 (University College London, Human Monoclonal Antibody against Rhesus D Antigen).
While the use of monoclonal antibodies has many advantages compared to the use of pools of polyclonal antibodies, it may, on the other hand, prove to be difficult to obtain an effective monoclonal antibody. In fact, it has been found, in the context of the invention, that the Fcγ fragment of the immunoglobulin obtained must have very particular properties in order to be able to interact with and activate the receptors of effector cells (macrophage, TH lymphocyte and NK).
The biological activity of certain G immunoglobulins is dependent on the structure of the oligosaccharides present on the molecule, and in particular on its Fc component. IgG molecules of all human and murine subclasses have an N-oligosaccharide attached to the CH2 domain of each heavy chain (at residue Asn 297 for human IgGs). The influence of this glycan-containing residue on the ability of the antibody to interact with effector molecules (Fc receptors and complement) has been demonstrated. Inhibiting glycosylation of a human IgG1, by culturing in the presence of tunicamycin, causes, for example, a 50-fold decrease in the affinity of this antibody for the FcγRI receptor present on monocytes and macrophages (Leatherbarrow et al., 1985). Binding to the FcγRIII receptor is also affected by the loss of carbohydrates on IgG, since it has been described that a nonglycosylated. IgG3 is incapable of inducing lysis of the ADCC type via the FcγRIII receptor of NK cells (Lund et al., 1990).
However, beyond the necessary presence of these glycan-containing residues, it is more precisely the heterogeneity of their structure which may result in differences in the ability to initiate effector functions. Galactosylation profiles which are variable depending on individuals (human serum IgG1s) have been observed. These differences probably reflect differences in the activity of galactosyltransferases and other enzymes between the cellular clones of these individuals (Jefferis et al., 1990). Although this normal heterogeneity of post-translational processes generates various glycoforms (even in the case of monoclonal antibodies), it may lead to atypical structures associated with certain pathological conditions, such as rheumatoid arthritis or Crohn's disease, for which a considerable proportion of agalactosylated residues have been demonstrated (Parekh et al., 1985).
The glycosylation profile of the purified molecule is the consequence of multiple effects, some parameters of which have already been studied. The protein backbone of IgGs, and in particular amino acids in contact with the terminal N-acetylglucosamine (GlcNAc) and galactose residues of the mannose α-1,6 arm (aa 246 and 258 of IgGs), may explain the existence of preferential structures (galactosylation), as shown in the study carried out on murine and chimeric IgGs of different isotypes (Lund et al., 1993).
The differences observed also reveal specificities related to the species and to the cell type used for producing the molecule. Thus, the conventional structure of the N-glycans of human IgGs reveals a significant proportion of bi-antennary types with a GlcNAc residue in the bisecting position, this being a structure which is absent in antibodies produced by murine cells. Similarly, the sialic acid residues synthesized by the CHO (Chinese Hamster Ovary) line are exclusively of the α-2,3 type, whereas they are of the α-2,3 and α-2,6 type with murine and human cells (Yu Ip et al., 1994). Immunoglobulin production in expression systems other than those derived from mammals may introduce much more important modifications, such as the presence of xylose residues produced by insect cells or plants (Ma et al., 1995).
Other factors, such as the cell culture conditions (including the composition of the culture medium, the cell density, the pH, the oxygenation), appear to have an effect on glycosyltransferase activity in the cell and, consequently, on the glycan structure of the molecule (Monica et al., 1993; Kumpel et al., 1994 b).
Now, in the context of the present invention, it has been found that a structure of the bi-antennary type, with short chains, a low degree of sialylation, and nonintercalated terminal mannoses and/or terminal GlcNAcs, is the common denominator for glycan structures which confer strong ADCC activity on monoclonal antibodies. A method for preparing such antibodies capable of activating effector cells via FcγRIII, in particular anti-Rh(D) antibodies, has also been developed.
Blood group antigens are classified in several systems depending on the nature of the membrane-bound molecules expressed at the surface of red blood cells. The Rhesus (Rh) system comprises 5 molecules or antigens: D, C, c, E and e (ISSITT, 1988). The D antigen is the most important of these molecules because it is the most immunogenic, i.e. it can induce the production of anti-D antibodies if Rh-D-positive red blood cells are transfused into Rh-negative individuals.
The D antigen is normally expressed in 85% of Caucasian individuals, these people are termed “Rh-positive;” 25% of these individuals are therefore Rh-negative, i.e. their red blood cells do not exhibit any D antigen. D antigen expression exhibits certain variants which may be linked either to a weak antigenic density, reference is then made to weak D antigens, or to a different or partial antigenicity, reference is then made to partial D antigens. The weak D characteristic is characterized in that it is a normal antigen, but the number of sites thereof per red blood cell is decreased more or less considerably; this characteristic is transmissible according to Mendelian laws. Partial D phenotypes have been discovered in Rh-D-positive individuals who have anti-D serum antibodies; these partial D antigens can therefore be characterized as having only part of the mosaic. Studies carried out with polyclonal and monoclonal antibodies have made it possible to define 7 categories of partial D antigens with at least 8 epitopes constituting the D antigen being described (LOMAS et al., 1989; TIPETT 1988).
The importance of anti-Rh D antibodies became apparent with the discovery of the mechanisms leading to hemolytic disease of the newborn (HDN). This corresponds to the various pathological conditions observed in some fetuses or in some newborn babies when there is a feto-maternal blood group incompatibility which is responsible for the formation of maternal anti-Rh D antibodies capable of crossing the placental barrier. In fact, fetal Rh-positive red blood cells passing into an Rh-negative mother can lead to the formation of anti-D antibodies.
After immunization of the Rh-negative mother, the IgG class anti-D antibodies are capable of crossing the placental barrier and of binding to the fetal Rh-positive red blood cells. This binding leads to the activation of immunocompetent cells via their surface Fc receptors, thus inducing hemolysis of the sensitized fetal red blood cells. Depending on the strength of the reaction, several degrees of seriousness of HDN can be observed.
An HDN diagnosis can be carried out before and after birth. Prenatal diagnosis is based on the development of the anti-D antibody level in the mother using several immunohematological techniques. Post-partum diagnosis may be carried out using an umbilical cord blood sample, analyzing the following parameters: determining the blood groups of the fetus and of the father; searching for anti-D antibodies; assaying the hemoglobin and the bilirubin.
Prophylactic treatment for HDN is currently systematically given to all women with an Rh-negative blood group who have given birth to an Rh-positive child, with injections of human anti-D immunoglobulin. The first real immunoprophylaxis trials began in 1964. For the prevention to be effective, the immunoglobulin must be injected before the immunization, i.e. within the 72 hours following the birth, and the antibody doses must be sufficient (10 μg of anti-D antibodies per 0.5 ml of Rh+ red blood cells).
Several anti-D monoclonal antibodies have been the subject of therapeutic assessment: BROSSARD/FNTS 1990 (not published); THOMSON/IBGRL 1990; KUMPEL/IBGRL 1994; BELKINA/Institute of hematology, Moscow, 1996; BIOTEST/LFB 1997 (not published). The clinical effectiveness of the antibodies in inducing clearance of Rh(D)-positive red blood cells was assessed in Rh(D)-negative volunteers.
A single IgG1 antibody showed an effectiveness equivalent to that of anti-D polyclonal immunoglobulins, but only in some patients (KUMPEL et al., 1995).
The invention proposes to provide monoclonal antibodies which reply to the abovementioned problems, i.e. antibodies selected using an assay of the ADCC type specific for the antibody and/or the antibodies having a glycan structure required for obtaining good effectiveness.